Re: [PATCH v6 0/8] crypto: x86: Fix indirect function call casts

Eric Biggers
2019-11-22T02:21:08Z

On Thu, Nov 21, 2019 at 05:03:26PM -0800, Kees Cook wrote:
> v6:
> - minimize need for various internal casts (ebiggers)
> - clarify comments (ebiggers)
> - switch all context pointers to const (ebiggers)
> v5: https://lore.kernel.org/lkml/20191113182516.13545-1-keescook@chromium.org
> v4: https://lore.kernel.org/lkml/20191111214552.36717-1-keescook@chromium.org
> v3: https://lore.kernel.org/lkml/20190507161321.34611-1-keescook@chromium.org
>
> Hi,
>
> Now that Clang's CFI has been fixed to do the right thing with extern
> asm functions, this patch series is much simplified. Repeating patch
> 1's commit log here:
>
> The crypto glue performed function prototype casting to make indirect
> calls to assembly routines. Instead of performing casts at the call
> sites (which trips Control Flow Integrity prototype checking), switch
> each prototype to a common standard set of arguments which allows the
> incremental removal of the existing macros. In order to keep pointer
> math unchanged, internal casting between u128 pointers and u8 pointers
> is added.
>
> With this series (and the Clang LTO+CFI series) I am able to boot x86
> with all crytpo selftests enabled without tripping any CFI checks.
>
> Thanks!
>
> -Kees
>
> Kees Cook (8):
> crypto: x86/glue_helper: Regularize function prototypes
> crypto: x86/serpent: Remove glue function macros usage
> crypto: x86/camellia: Remove glue function macro usage
> crypto: x86/twofish: Remove glue function macro usage
> crypto: x86/cast6: Remove glue function macro usage
> crypto: x86/aesni: Remove glue function macro usage
> crypto: x86/glue_helper: Remove function prototype cast helpers
> crypto, x86/sha: Eliminate casts on asm implementations

This patchset doesn't actually compile until patch 6/8, due to
-Werror=incompatible-pointer-types in the kernel's top-level Makefile. It's
generally expected that every kernel commit compiles, and I'm not sure it's a
good idea to allow any exceptions.

The easiest solution would be to just squash the first 6 patches together into
one big patch.

Alternatively, 'ccflags-y := -Wno-error=incompatible-pointer-types' could be
added to arch/x86/crypto/Makefile in patch 1 and removed in patch 7.

- Eric